Viral phenomenon: Ancient microbe invaded human DNA

Humans carry in their genome the relics of an animal virus that infected their forerunners at least 40 million years ago, according to research published Wednesday by the British science journal Nature.

The invader is called bornavirus, a brain-infecting pathogen that was first identified in 1970s.

The disease owes its name to the German town of Borna, where a regiment of cavalry horses was wiped out in 1885 by a mysterious "heated head" disease.